INTEGUMENTARY SYSTEM

The integumentary system comprises the skin with its adnexal structures (e.g. hair and glands), horns, hoofs, claws, and other modifications of the epithelial covering of the body

All the components of integument are modification of the surface epithelium.

SKIN

largest organ in the body: 12-15% of body weight, with a surface area of 1-2 meters sq.

Continuous with, but structurally distinct from mucous membranes that line the mouth, anus, urethra, and vagina.

Two distinct layers occur in the skin:1. Epidermis.2.Dermis

1.Epidermis:Avascular layer, no nerve endings.Divided histologically into (deep to

superficial):1. Stratum basale-mitotically active cells.2. Stratum spinosum-spiny appearance due

to inter-cellular bridges.3. Stratum granulosum-spindle shaped cells4. Stratum lucidum5. Stratum corneum-layer of dead flattened

cells.

2. The dermis A connective tissue layer under the

epidermis, and contains nerve endings, sensory receptors, capillaries, lymphatics and elastic fibers.

3. HypodermisA layer of loose connective tissues

seperating skin from underlying tissues.

Allows movement of skin without tearing.

Varying amount of fat is found in this layer.

FUNCTIONS OF SKIN

ProtectionThermoregulationSensory receptionWater balanceSynthesis of vitamins and hormonesAbsorption of materials.

Protection:Serve as a barrier to the entry of

microbes.Prevent water and extracellular fluid

loss. Acidic secretions from skin glands also

retard the growth of fungi. Melanocytes - second barrier:

protection from the damaging effects of ultraviolet radiation.

Skin and Water balance:Evaporation Sweating In hot weather up to 4 liters per

hour can be lost by these mechanisms.

Skin damaged by burns is less effective at preventing fluid loss, often resulting in a possibly life threatening problem if not treated.

Skin and Thermoregulation:Heat and cold receptors - located in the

skin. When the body temperature rises-the

hypothalamus sends a nerve signal to the sweat-producing skin glands-release about 1-2 liters of water per hour- cooling the body.

The hypothalamus - causes dilation of the blood vessels of the skin-more blood to flow - heat convected away from the skin surface.

When body temperature falls-sweat glands constrict and sweat production decreases.

If the body temperature continues to fall, the body will engage in thermiogenesis, or heat generation, by raising the body's metabolic rate and by shivering.

Skin and Sensory Reception :Sensory receptors -pain, pressure

(touch), and temperature. Deeper within the skin are

Meissner's corpuscles, -in the tips of the fingers and lips-very sensitive to touch.

Pacinian corpuscles respond to pressure.

Skin and Synthesis:Skin cells synthesize melanin and

carotenes, which give the skin its color.

Also assists in the synthesis of vitamin D.

Children lacking sufficient vitamin D develop bone abnormalities known as rickets.

Skin and absorption: Skin -selectively permeable to fat-soluble

substances such as vitamins A, D, E, and K, as well as steroid hormones such as estrogen.

Enter the bloodstream through the capillary networks in the skin.

Patches have been used to deliver a number of therapeutic drugs in this manner. These include estrogen, scopolamine (motion sickness), nitroglycerin (heart problems), and nicotine (for those trying to quit smoking).

GLANDS

Sebaceous gland-Empty oily secretion called sebum

into hair follicles.Some empty directly onto the

surface of the skin-ear cannal, around anus, in the penis, prepuce, vulva.

Specialized sebaceous glands:Marking glandsCharacteristic of their species.Sheep:1.Infra-orbital pouches-in the medial

canthus of eyes2.Inter-digital pouches-on the midline

above the hooves.3.Inguinal pouches-Naer the base of

the udder or scrotum.

Goat-horn glands- Located Caudal to the base of the horns. Secretions becomes more in breeding seasons giving pungent smell of bucks.

Pigs-carpal glands- Located on the medial aspect of the carpus.

Sudoriferous glands/ Sweat glands

Tubular glands found all over the body.

Well developed in horses.Sparse in cow, sheep and pigs.Mammary gland is modification of

sweat gland.

HAIRDefining characteristic of mammalsThree main types of hair on domestic

mammals:1.Guard hairs, which form the smooth

outer coat 2.Woolhairs, also called the undercoat,

which are fine and often curly.3.Tactile hairs, long stiff hairs with

specialized innervation that renders them effective as organs of touch.

An individual hair arises from a modification of the epidermis, the hair follicle.

An individual hair has a medulla at its center, surrounded by a scaly cortex, outside of‘ which is a thin cuticle.

The bulk of the hair comprises the cortex.

All parts of the hair are‘ composed of compressed, keratinized epithelial cells.

The amount and type of melanin in cortical cells determine whether the hair will be black, brown, or red.

Wool hairs lack a medulla or have only a very small one, accounting for their fine, flexible nature.

Cuticle is a single layer of thin, clear cells covering the cortex.

Arrector pili muscle-A tiny bundle of smooth muscle that extends from the deep portion of the hair follicle at an angle towards epidermis.

Contraction of this muscle raises the hair to 90 degrees. This increases the insulation property during cold exposure and also increases apparent size of the animal to the oponent during fight-or-flight reaction.

Contraction of this muscle also compresses the sebaceous glands and helps in emptying it.

MODIFIED EPIDERMIS

HoofA defining characteristic of

ungulatesUngulates- well-developed hoof

associated with the distal phalanx. Although the hoofs of pigs,

ruminants, and horses differ significantly in their gross appearance, they share certain features.

COMMON FEATURES Have an outer avascular epidermal layer

and an inner vascularized dermis The dermis of hoofs and horns are

commonly called as corium. The outside -covered by a thin, waxy layer

called the periople. The thick hoof wall grows from a belt of

epidermis at the coronary band. The deep side of the hoof wall is intimately

connected to the underlying corium, which blends with the periosteum of the distal phalanx.

HORNS

Formed over the cornual process-from the frontal bone of the skull

Animals that lack horns naturally are called polled.

The corium of the horn completely envelops the comual process and blends with its periosteum.

The hom itself consists of dense keratin, much like the hoof wall, and elongates from the base.

DewclawsThe accessory digits Ruminant dewclaws do not bear

weight. Dairymen occasionally have the

medial dewclaws on the pelvic limbs removed-prophylactic measure against injury to the udder

Porcine dewclaws occasionally make contact with the ground when the pig stands on soft surfaces.

Chestnuts and ErgotsChestnuts are hornlike growths on

the medial sides of horses' limbs. Ergots are small projections of

cornifined epithelium in the center of the palmar (plantar)part of the fetlock of the horse. The tuft of hair at the fetlock hides the ergot in most instances